The invention is directed to a furnace for melting and casting a charge of material. Without limitation, such material may include a metal, alloy, or the like. In particular the invention relates to such a furnace which comprises a unitary or single chamber in which the charge is continuously melted and metal ingots and the like continuously produced from the same mold or molds and continuously collected in an appropriate discharge bin without opening the chamber during the continuous process. Such chamber may be subjected to vacuum or partial vacuum or an inert atmosphere, if desired.
Generally, in prior art furnaces a charge of metal is fed to a crucible which is subjected to induction heating for the purpose of reducing the charge to a molten state. Subsequently, the molten metal is poured into a mold for casting and allowed to solidify as the metal cools. When the process is complete, the solidified metal or ingot is removed from the mold, and the process may then be repeated. It is often desirable to melt and cast the metal under a vacuum, or in an inert atmosphere, and to this end the crucible, mold and ingot removal means may be positioned in appropriate chambers. In order to facilitate the processing of such ingots with minimum furnace shut down time, known prior art furnaces may comprise a plurality of chambers equipped with sealed closures therebetween. For example, in Moore, U.S. Pat. No. 2,625,719, a vacuum casting apparatus is described which includes a vacuum chamber in which metal to be melted is fed, another vacuum chamber in which such metal is melted, and a third vacuum chamber in which an ingot is cast from the molten metal. The Moore structure also includes a plurality of vacuum-tight closures or valves, there being a first closure through which metal is introduced into the feeding chamber, a second closure between the feeding and furnace or melting chambers, a third closure between the furnace and casting chambers and a fourth closure for permitting the removal of the ingot from the casting chamber. In the process associated with such a prior art furnace, the seal at the first closure must be broken and the vacuum vented each time a fresh supply of metal is inserted. Subsequently, the first closure is resealed and the feeding chamber is evacuated to obtain the desired vacuum. The metal is then advanced through the feeding, melting and casting chambers by opening and closing the second and third vacuum-tight closures. As each individual ingot is cast and cooled, the vacuum-tight connection which forms the fourth closure is broken and the mold is removed. Before the process may be repeated, the seal at the first closure must once again be broken, the vacuum in the feeding chamber vented and a fresh supply of metal inserted therein, and the feeding chamber once again resealed and evacuated to obtain the desired vacuum. At the other end of the process, an empty mold must be replaced in the casting chamber, and the casting chamber must be sealed and evacuated to obtain the desired vacuum.
Other known prior art furnaces useful in producing cast metals may comprise a plurality of vacuum augmented chambers equipped with vacuum tight or sealed closures between select of such chambers. For example, the vacuum furnace described in Franks et al, U.S. Pat. No. 2,854,228 comprises a first vacuum furnace or melting chamber and a second vacuum chamber which includes the mold per se. The first and second chambers are not sealed relative to each other. However, each chamber is provided with separate evacuation means. A third vacuum chamber is provided for loading and unloading a launder, and such chamber is isolated from the vacuum furnace by means of a vacuum closure. To load or unload the launder, the vacuum seal or closure to the third chamber must be broken and the vacuum therein vented. The third chamber is provided with a separate evacuation means to evacuate the third chamber upon resealing thereof. Franks et al. appears to depict a structure similar to that described in Moore wherein as each individual ingot is cast and cooled, a vacuum-tight connection is broken to remove the mold thereby necessitating resealing and repeated evacuation each time the process is repeated.
A similar prior art furnace is described in Bussard et al., U.S. Pat. No. 3,014,255 wherein a first melting chamber is provided having a second chamber positioned underneath for casting, the chambers being evacuated by the same pump to create the necessary vacuum. An antechamber is provided with an inner airtight gate or closure leading to the casting chamber and an outer airtight gate leading to the outside. An exit chamber is provided and is also provided with an inner airtight gate or closure leading to the casting chamber and an outer airtight gate leading to the outside. The antechamber and exit chamber are also provided with evacuation means to provide vacuum chambers as required. In operation, molten metal is poured from the melting chamber into molds positioned upon carriage means in the casting chamber. The inner airtight gates or closures are opened to remove to the exit chamber the carriage and filled molds and to reposition into the casting chamber another carriage carrying unfilled molds. Such inner gates are then closed and the outer gates are opened to remove from the exit chamber the carriage and filled molds and to position into the antechamber a carriage with unfilled molds. The outer gates are then closed, and the antechamber and exit chamber are again subjected to evacuation to create the necessary vacuum. This process is repeated each time the molds positioned in the casting chamber are filled.
Other known prior art describes vacuum augmented furnaces comprising a plurality of vacuum chambers separated by sealed closures. In such furnaces, the vacuum is vented in at least one of the chambers each time the respective mold is emptied and such chamber requires additional vacuum augmentation prior to each time the mold is refilled and emptied again. Such structures are described in Tingquist et al., U.S. Pat. No. 3,336,971, Taylor et al., U.S. Pat. No. 3,554,268 and Bly et al., U.S. Pat. No. 3,635,791.
Problems resulting from the use of various prior art furnaces include the need to provide sealed gates or closures between isolated chambers and means to open and close such closures. In addition, in vacuum furnaces evacuation means must be provided for each isolated chamber. Such means will include separate vacuum lines and may require the use of separate vacuum sources or pumps. In operation, each time the mold or molds are emptied the vacuum is vented in at least one of the chambers, and such chamber will require additional vacuum augmentation prior to each time the mold or molds are refilled for further casting.
Another problem incurred in prior art furnaces is that the electrode crucible and mold tend to deteriorate as a result of the various stresses to which such equipment is exposed during use thereof. Such deterioration may be caused by, for example, continuous thermal expansion and contraction as temperatures continuously change throughout the melting and casting process, as well as thermal degradation.
Accordingly, it is an object of this invention to provide a furnace for melting, casting and discharging a charge of metal a unitary chamber.
Another object of this invention is to provide a furnace for melting, casting and discharging a charge of metal wherein the furnace does not require sealed gates or closures between isolated chambers, or means to open and close such closures. Still another object of this invention is to provide a furnace for melting, casting and discharging a charge of metal wherein the charge of metal does not require being fed through melting, casting and discharging chambers, one or more of which are sealed relative to others.
A further object of this invention is to provide a furnace for melting, casting and discharging a charge of metal under a vacuum wherein the furnace does not require the use of separate evacuation means for separate isolated vacuum chambers.
Still a further object of this invention is to provide a furnace for melting, casting and discharging a charge of metal under a vacuum in a unitary vacuum chamber wherein a crucible and mold may be emptied and refilled without venting the vacuum.
Yet another object of this invention is to provide a furnace for melting, casting and discharging a charge of metal under a vacuum in a unitary vacuum chamber wherein a crucible and mold may be emptied without subjecting the vacuum chamber to additional vacuum augmentation prior to each time the crucible and mold are refilled for further casting.
Another object of this invention is to provide an electrode which will resist the stresses to which it is subjected in a furnace used to melt, cast and discharge a charge of metal.
A further object of this invention is to provide a crucible which will resist the stresses to which it is subjected in a furnace used to melt, cast and discharge a charge of metal.
Yet another object of this invention is to produce a mold which will resist the stresses to which it is subjected in a furnace used to melt, cast and discharge a charge of metal.